Does anyone know roughly how much it would cost to have a new engine professionally installed? Also, what would be needed to switch out a 4.6L with a 5.4L?

those engines are crazy expensive. you would save quite a bit of money by selling your expedition and buying one with a 5.4L. last i heard it's about $7000 can. for a 5.4 and probably around $1400 to get it put in but if it's a swap you need the prober intake, computer, wiring harness, exhaust manifolds, and probably a whole list of other parts. so basicaly it would cost more than a 98 expedition with a 5.4L in it already.